A human cDNA clone has been isolated that encodes a new immunoglobulin superfamily member, AAMP. Its sequence predicts a novel 45.7 kDa protein with a potential transmembrane domain, immunoglobulin domains, and a heparin binding consensus sequence near the amino terminus. Anti-peptide antibodies, created to react with specific regions of AAMP's predicted sequence, react-positively with recombinant AAMP protein thus confirming its predicted sequence. The immunoglobulin-like domains of AAMP are homologous with multiple domains from immunoglobulin superfamily members, including the "deleted in colon carcinoma" (DCC) protein, neural cell adhesion molecule (NCAM) and intercellular cell adhesion molecule (ICAM). Single, 1.6 kilobase mRNA transcripts of AAMP are present in many adult and fetal tissues. Studies of the RNA message levels in T cell activation, a known modulating event for adhesive proteins, showed marked augmentation of AAMP with peak levels at 24 hours. A peptide (P189), derived from the predicted heparin binding domain of AAMP, binds heparin and elicits heparin dependent cell aggregation. Substituted or scrambled forms of this peptide could not induce comparable human melanoma cell aggregation. Immobilized P189 and its variants that contained the heparin binding consensus sequence mediated cell attachment significantly more than the variants that lacked the consensus sequence. Heparin abolished the cell attachment activity of P189. AAMP can potentially mediate cell- cell and cell-matrix interactions. An anti-peptide, polyclonal antibody specific for P189 reacts with a protein that is comparable in size to AAMP in human brain tissue and in activated T lymphocytes. When aliquots of cell lysates from a time course of T cell activation are standardized either according to cell number or amount of protein, the expression of the 56 kDa anti-P189 specific protein increases after 72 hours.